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Kinetochores
A kinetochore (, ) is a disc-shaped protein structure associated with duplicated chromatids in eukaryotic cells where the spindle fibers attach during cell division to pull sister chromatids apart. The kinetochore assembles on the centromere and links the chromosome to microtubule polymers from the mitotic spindle during mitosis and meiosis. The term kinetochore was first used in a footnote in a 1934 Cytology book by Lester W. Sharp and commonly accepted in 1936. Sharp's footnote reads: "The convenient term ''kinetochore'' (= movement place) has been suggested to the author by J. A. Moore", likely referring to John Alexander Moore who had joined Columbia University as a freshman in 1932. Monocentric organisms, including vertebrates, fungi, and most plants, have a single centromeric region on each chromosome which assembles a single, localized kinetochore. Holocentric organisms, such as nematodes and some plants, assemble a kinetochore along the entire length of a chromosome. Ki ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Kinetochore
A kinetochore (, ) is a disc-shaped protein structure associated with duplicated chromatids in eukaryotic cells where the spindle fibers attach during cell division to pull sister chromatids apart. The kinetochore assembles on the centromere and links the chromosome to microtubule polymers from the mitotic spindle during mitosis and meiosis. The term kinetochore was first used in a footnote in a 1934 Cytology book by Lester W. Sharp and commonly accepted in 1936. Sharp's footnote reads: "The convenient term ''kinetochore'' (= movement place) has been suggested to the author by J. A. Moore", likely referring to John Alexander Moore who had joined Columbia University as a freshman in 1932. Monocentric organisms, including vertebrates, fungi, and most plants, have a single centromeric region on each chromosome which assembles a single, localized kinetochore. Holocentric organisms, such as nematodes and some plants, assemble a kinetochore along the entire length of a chromosome. Ki ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Kinetochore Vertebrates-en
A kinetochore (, ) is a disc-shaped protein structure associated with duplicated chromatids in eukaryotic cells where the spindle fibers attach during cell division to pull sister chromatids apart. The kinetochore assembles on the centromere and links the chromosome to microtubule polymers from the mitotic spindle during mitosis and meiosis. The term kinetochore was first used in a footnote in a 1934 Cytology book by Lester W. Sharp and commonly accepted in 1936. Sharp's footnote reads: "The convenient term ''kinetochore'' (= movement place) has been suggested to the author by J. A. Moore", likely referring to John Alexander Moore who had joined Columbia University as a freshman in 1932. Monocentric organisms, including vertebrates, fungi, and most plants, have a single centromeric region on each chromosome which assembles a single, localized kinetochore. Holocentric organisms, such as nematodes and some plants, assemble a kinetochore along the entire length of a chromosome. Ki ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Spindle Checkpoint
The spindle checkpoint, also known as the metaphase-to-anaphase transition, the spindle assembly checkpoint (SAC), the metaphase checkpoint, or the mitotic checkpoint, is a cell cycle checkpoint during mitosis or meiosis that prevents the separation of the duplicated chromosomes (anaphase) until each chromosome is properly attached to the spindle. To achieve proper segregation, the two kinetochores on the sister chromatids must be attached to opposite spindle poles (bipolar orientation). Only this pattern of attachment will ensure that each daughter cell receives one copy of the chromosome. The defining biochemical feature of this checkpoint is the stimulation of the anaphase-promoting complex by M-phase cyclin-CDK complexes, which in turn causes the proteolytic destruction of cyclins and proteins that hold the sister chromatids together. Overview and importance The beginning of metaphase is characterized by the connection of the microtubules to the kinetochores of the chrom ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Spindle Fibers
In cell biology, the spindle apparatus refers to the cytoskeletal structure of eukaryotic cells that forms during cell division to separate sister chromatids between daughter cells. It is referred to as the mitotic spindle during mitosis, a process that produces genetically identical daughter cells, or the meiotic spindle during meiosis, a process that produces gametes with half the number of chromosomes of the parent cell. Besides chromosomes, the spindle apparatus is composed of hundreds of proteins. Microtubules comprise the most abundant components of the machinery. Spindle structure Attachment of microtubules to chromosomes is mediated by kinetochores, which actively monitor spindle formation and prevent premature anaphase onset. Microtubule polymerization and depolymerization dynamic drive chromosome congression. Depolymerization of microtubules generates tension at kinetochores; bipolar attachment of sister kinetochores to microtubules emanating from opposite cell pole ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Mitotic Spindle
In cell biology, the spindle apparatus refers to the cytoskeletal structure of eukaryotic cells that forms during cell division to separate sister chromatids between daughter cells. It is referred to as the mitotic spindle during mitosis, a process that produces genetically identical daughter cells, or the meiotic spindle during meiosis, a process that produces gametes with half the number of chromosomes of the parent cell. Besides chromosomes, the spindle apparatus is composed of hundreds of proteins. Microtubules comprise the most abundant components of the machinery. Spindle structure Attachment of microtubules to chromosomes is mediated by kinetochores, which actively monitor spindle formation and prevent premature anaphase onset. Microtubule polymerization and depolymerization dynamic drive chromosome congression. Depolymerization of microtubules generates tension at kinetochores; bipolar attachment of sister kinetochores to microtubules emanating from opposite cell pol ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Holocentric Chromosome
Holocentric chromosomes are chromosomes that possess multiple kinetochores along their length rather than the single centromere typical of other chromosomes. They were first described in cytogenetic experiments in 1935. Since this first observation, the term holocentric chromosome has referred to chromosomes that: i) lack the primary constriction corresponding to the centromere observed in monocentric chromosomes; and ii) possess multiple kinetochores dispersed along the entire chromosomal axis, such that microtubules bind to the chromosome along its entire length and move broadside to the pole from the metaphase plate. Holocentric chromosomes are also termed ''holokinetic'', because, during cell division, the sister chromatids move apart in parallel and do not form the classical V-shaped figures typical of monocentric chromosomes. Holocentric chromosomes have evolved several times during both animal and plant evolution, and are currently reported in about eight hundred diverse speci ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Microtubule
Microtubules are polymers of tubulin that form part of the cytoskeleton and provide structure and shape to eukaryotic cells. Microtubules can be as long as 50 micrometres, as wide as 23 to 27 nm and have an inner diameter between 11 and 15 nm. They are formed by the polymerization of a dimer of two globular proteins, alpha and beta tubulin into protofilaments that can then associate laterally to form a hollow tube, the microtubule. The most common form of a microtubule consists of 13 protofilaments in the tubular arrangement. Microtubules play an important role in a number of cellular processes. They are involved in maintaining the structure of the cell and, together with microfilaments and intermediate filaments, they form the cytoskeleton. They also make up the internal structure of cilia and flagella. They provide platforms for intracellular transport and are involved in a variety of cellular processes, including the movement of secretory vesicles, organell ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Mad2
Mad2 (mitotic arrest deficient 2) is an essential spindle checkpoint protein. The spindle checkpoint system is a regulatory system that restrains progression through the metaphase-to-anaphase transition. The Mad2 gene was first identified in the yeast ''S. cerevisiae'' in a screen for genes which when mutated would confer sensitivity to microtubule poisons. The human orthologues of Mad2 (MAD2L1 and MAD2L2) were first cloned in a search for human cDNAs that would rescue the microtubule poison-sensitivity of a yeast strain in which a kinetochore binding protein was missing. The protein was shown to be present at unattached kinetochores and antibody inhibition studies demonstrated it was essential to execute a block in the metaphase-to-anaphase transition in response to the microtubule poison nocodazole. Subsequent cloning of the ''Xenopus laevis'' orthologue, facilitated by the sharing of the human sequence, allowed for the characterization of the mitotic checkpoint in egg extracts. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Mitosis
In cell biology, mitosis () is a part of the cell cycle in which replicated chromosomes are separated into two new nuclei. Cell division by mitosis gives rise to genetically identical cells in which the total number of chromosomes is maintained. Therefore, mitosis is also known as equational division. In general, mitosis is preceded by S phase of interphase (during which DNA replication occurs) and is often followed by telophase and cytokinesis; which divides the cytoplasm, organelles and cell membrane of one cell into two new cells containing roughly equal shares of these cellular components. The different stages of mitosis altogether define the mitotic (M) phase of an animal cell cycle—the division of the mother cell into two daughter cells genetically identical to each other. The process of mitosis is divided into stages corresponding to the completion of one set of activities and the start of the next. These stages are preprophase (specific to plant cells), prophase ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cell Division
Cell division is the process by which a parent cell (biology), cell divides into two daughter cells. Cell division usually occurs as part of a larger cell cycle in which the cell grows and replicates its chromosome(s) before dividing. In eukaryotes, there are two distinct types of cell division: a vegetative division (mitosis), producing daughter cells genetically identical to the parent cell, and a cell division that produces Haploidisation, haploid gametes for sexual reproduction (meiosis), reducing the number of chromosomes from two of each type in the diploid parent cell to one of each type in the daughter cells. In cell biology, mitosis (Help:IPA/English, /maɪˈtoʊsɪs/) is a part of the cell cycle, in which, replicated chromosomes are separated into two new Cell nucleus, nuclei. Cell division gives rise to genetically identical cells in which the total number of chromosomes is maintained. In general, mitosis (division of the nucleus) is preceded by the S stage of interph ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Meiosis
Meiosis (; , since it is a reductional division) is a special type of cell division of germ cells in sexually-reproducing organisms that produces the gametes, such as sperm or egg cells. It involves two rounds of division that ultimately result in four cells with only one copy of each chromosome ( haploid). Additionally, prior to the division, genetic material from the paternal and maternal copies of each chromosome is crossed over, creating new combinations of code on each chromosome. Later on, during fertilisation, the haploid cells produced by meiosis from a male and female will fuse to create a cell with two copies of each chromosome again, the zygote. Errors in meiosis resulting in aneuploidy (an abnormal number of chromosomes) are the leading known cause of miscarriage and the most frequent genetic cause of developmental disabilities. In meiosis, DNA replication is followed by two rounds of cell division to produce four daughter cells, each with half the number of chr ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Metaphase
Metaphase ( and ) is a stage of mitosis in the eukaryotic cell cycle in which chromosomes are at their second-most condensed and coiled stage (they are at their most condensed in anaphase). These chromosomes, carrying genetic information, align in the equator of the cell before being separated into each of the two daughter cells. Metaphase accounts for approximately 4% of the cell cycle's duration. Preceded by events in prometaphase and followed by anaphase, microtubules formed in prophase have already found and attached themselves to kinetochores in metaphase. In metaphase, the centromeres of the chromosomes convene themselves on the ''metaphase plate'' (or ''equatorial plate''), an imaginary line that is equidistant from the two centrosome poles. This even alignment is due to the counterbalance of the pulling powers generated by the opposing kinetochore microtubules, analogous to a tug-of-war between two people of equal strength, ending with the destruction of B cyclin. In ce ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
